Oval port H89 heads have way larger inlet and exhaust valves from factory
ports larger but smaller than oversized GX yet just right for all round
performance much like the big port FIA heads that where made later with
smaller ports as it improves the midrange torque.
The oval ports also have higher port position and really are great addition
to a bigger A series or high performance engine.
To get a round port to flow close to an Oval port head theres is quite alot
of wallet clearing and custom manifolding not designed for big round ports.